An antigenic polysaccharide has been isolated from rheumatoid synovial fluid, synovial fluid leukocytes, articular cartilage and plasma. This antigen is immunologically identical to a polysaccharide containing antigen present in Propionibacterium acnes, a ubiquitous human pathogenic anaerobe. The bacterial and human extracted antigens also have common biochemical and physical characteristics such as molecular weight (by gel filtration) approximately 150,000, resistance to heat and proteolytic enzymatic digestion, and sensitivity to periodate oxidation. Isolation of the tissue antigen requires extraction with either phenol-water or an immune complex dissociation method before it can be identified by counter-immunoelectrophoresis against rabbit antisera or human sera containing antibody. Concentrations of this antigen range from 1-10 mug/ml in synovial fluid and plasma to as high as 400 mug/g in articular cartilage. The purification of the antigen from P. acnes in conjunction with the one from rheumatoid tissues to constant specific immunological response is proposed. Immunoaffinity-chromatography will be used to speed up the isolation and purification of this material. The thus purified antigens will be analyzed for their quantitative composition in respect to building blocks (amino acids, monosaccharides, polyols and inorganic substituents) as well as for their covalently linked structure. Smith degradation in combination with hydrazinolysis and nitrous acid fragmentation will be used. Aldehydic fragments including reducing sugars will be analyzed and identified as amino derivatives after their reductive amination. High performance cation exchange chromatography with flourescence detection has been shown to be equivalent to gas chromatographic sensitivity. The antigenically important features will be determined correlating the loss of specific building blocks and decrease in immune response with the emergence of new amino alcohols after periodate oxidation and reductive amination.